Thomas, the eldest son of Colonel Thomas Blackborne Hildyard , was educated at Eton and then Oxford. Born at his family seat of Flintham Hall, Nottinghamshire, Hildyard’s connections brought him significant local influence. His father died in 1830, when Thomas was a boy, and the family's estates at Flintham, Screveton and Winestead were administered by his mother and his uncles the Rev. Levett Thoroton and Colonel Robert Thoroton during his minority. They managed to secure Flintham Hall against Colonel Hildyard's creditors by selling his Lincolnshire estates. On coming of age in 1842 Thomas married Anne Margaret, daughter of Colonel John Staunton Rochfort of Cloghrenane, county Carlow.

In 1846 he entered political life, having been elected as Conservative M.P. for South Nottinghamshire. The election was a bitterly fought one. Hildyard was strongly supported by the 4th Duke of Newcastle under Lyne in spite of the fact that Newcastle’s son, the Earl of Lincoln, was his opponent. Lincoln attacked Hildyard’s youth and inexperience, but the ‘young squire’ still defeated him by a majority of almost 700.

Hildyard held South Nottinghamshire from 1846 until 1852. He was re-elected in 1866. He then continued to represent the South Nottinghamshire constituency until his retirement in 1885. He also served as a J.P. and Deputy Lieutenant for Nottinghamshire, and was High Sheriff of Nottingham in 1862.

He was responsible for the Italianate extension of Flintham Hall by the Nottingham architect T.C. Hine between 1853-1857. His rash spending forced him to live abroad for a time, to let Flintham Hall out to tenants, and in 1884 to sell the remaining Hildyard estates at Winestead in Yorkshire. Flintham itself was put up for sale in 1885 but no buyer was found.